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Full text of "The Morphology And Evolution Of The Apes And Man"

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Consequently the loss of the olfactory sense leads on to the second point of difference—the visual apparatus in Tarsius is better developed than in the Lemurs, but poorer than in the Anthropoidea. The overlapping of the visual fields is associated with binocular vision and a great increase in the visual cortex. The Anthropoidea are more highly evolved, for they have maculae lutese and incpmplete optic decussations, thus enabling them to focus objects on corresponding points on the retinae by moving their eyes alone. Tarsius has no maculae and its optic decussation is complete, so it moves its head as a whole to see objects properly. In the third place the papillary ridges on the palms and soles are more extensive than in the Lemurs, but more restricted than in the higher Primates. Hence the acuteness of the tactile sense is also intermediate in Tarsius.
From a study of comparative anatomy one can conclude that Tarsius is in some ways more primitive and in other ways more specialized than the Lemurs; but on the whole the specializations are fewer and slighter. As Professor Elliot Smith (149) says: " Tarsius, however, although on a distinctly higher plane of Primate development, has managed to escape extinction with fewer and slighter specializations than the Lemurs. Hence it has retained a much more generalized and obviously primitive structure along with the germs of the features that are distinctive of monkeys."